1. Technical Field
The present disclosure relates to a bump structure for a semiconductor device, and more particularly, to a new bump structure and a fabrication method thereof for fine pitch semiconductor package.
2. Discussion of Related Art
As personal computers, portable phones, personal information terminals and electronic products have become small, light and been functionalized, data processing capacity has greatly increased. In accordance with this tendency, a wafer level chip scale package to be very close to the size of a semiconductor chip is regarded in semiconductor packages.
Generally, in the wafer level chip scale package, a wafer is packaged and cut after a wafer fabrication process. As a result, a process of the wafer level chip scale package is much simpler than that of a general packaging process through die bonding, wire bonding and molding processes. Further, the wafer level chip scale package provides an advantage of forming solder bumps of all chips on a single wafer at once. Further, the wafer level chip scale package is capable of testing an operation of each chip on the wafer, thereby incurring less fabrication costs, compared to conventional general packages.
As the integration density of a semiconductor device gets larger and the size of the device gets smaller, bumps in semiconductor package becomes smaller and the distance between neighboring bumps becomes extremely narrow. Solder used as a general bump material has usually spherical shape, as shown in FIG. 1. Solder bump is transformed during reflow process into spherical shape, which causes the increase of horizontal width of a bump and resultantly reduces the distance between neighboring bumps. Thus, a spherical solder bump is not suitable for a semiconductor package with fine-pitch bumps.
Fine-pitch flip chip bump for a semiconductor package should be required to be formed in a cylindrical shape with high aspect ratio, and be fabricated without spreading out laterally in order to avoid a short between bumps.
Furthermore, there have been many defects in assembly of a package and a circuit board, such as dimple, or void in the contact point. Thus, an improved semiconductor package should be required in order to obtain reliability.